1. Field of the Invention
The present invention relates to an electronic musical instrument which is designed so that a waveshape calculation according to the Fourier calculation method is performed by switching it between the calculation of a waveshape varying with time and the calculation of a waveshape free from variations with time (which waveshape will hereinafter be referred to as a fixed waveshape), thereby to permit a rapid response to a tone variation or the like through the use of low-frequency clock pulses.
2. Description of the Prior Art
For obtaining a desired waveshape varying with time in response to the depression of a key on a keyboard, it is general practice in the prior art to calculate waveshape amplitude values at respective sample points by a waveshape calculation unit according to the Fourier calculation method. In this calculation, use is made of a system in which the waveshape calculator is activated by a change in a tone select switch such as a tablet, draw bar or the like and the states of the tone select switch and a key switch are sampled and then the waveshape calculation is conducted by the Fourier calculation method in real time. In this case, since the states of the key being depressed and the resulting tone are used as calculation elements for each calculation, the calculation period showing variations in the waveshape with time is lengthened, resulting in the likelihood of lessening the effect of a quick response to a tone variation. This can be avoided by reducing the calculation period through the use of sampling clock pulses of high frequency, but such sampling clock pulses must be subjected to high-speed processing, involving the use of expensive circuits.